Known brushcutters often employ an engine as a drive source. In the brushcutters, a drive force from the drive source is transmitted to a shaft in an operating rod via a centrifugal clutch. The drive force rotates an attachment such as a chip saw and a nylon cutter that is attached to an end of the shaft.
The centrifugal clutch includes: an attachment plate coupled to a crankshaft of the engine; a clutch shoe rotatably attached to the attachment plate, the clutch shoe rotating in accordance with centrifugal force; and a clutch drum frictionally engaged with the clutch shoe that is rotated radially outward, the clutch drum being connected with a base end of the shaft. The drive force is transmitted via the clutch shoe and the clutch drum that are mutually frictionally engaged.
The centrifugal clutch is disposed at an outer side of a cooling fan rotatably attached to the crankshaft and is entirely covered with a clutch housing. A bearing for supporting the shaft connected to the clutch drum is held within the clutch housing.
The clutch housing is made of metal or, alternatively, made of a synthetic resin in order to reduce the weight thereof. Clutch housings made of a synthetic resin are easily affected by a friction heat generated by the friction between the clutch shoe and the clutch drum.
Accordingly, when, for instance, lengthening a nylon head of a nylon cutter in order to mow a large amount of grasses within a short time, the load on the shaft is increased to cause continuous slip between the clutch drum and the clutch shoe, so that the temperature of the centrifugal clutch becomes high. Consequently, on account of radiation heat from the centrifugal clutch, the clutch housing may be heated beyond a softening temperature thereof to be deformed to cause dropoff of the bearing.
Accordingly, a large number of external-air inlet slits are provided on a typical clutch housing at a part corresponding to an outer circumference of the centrifugal clutch. In other words, the cooling air sucked by the cooling fan is inhaled through the slits so that the centrifugal clutch is cooled by the cooling air, thereby keeping the temperature of the centrifugal clutch from becoming excessively high (see, for instance, Patent Literature 1).